The index closed 15.57 points lower after gaining 5.5 points in the previous session.
Trading on the Ho Chi Minh Stock Exchange decreased by 0.35% to VND27.424 trillion ($1.09 billion).
The VN-30 basket, comprising the 30 largest capped stocks, saw all tickers fell.
GVR of Vietnam Rubber Group saw the biggest drop, plunging 2.84%, while CTG of state-owned lender VietinBank and MWG of electronics retail chain Mobile World both went down 2.71%.
MBB of state-owned MB Bank saw a 2.42% decline, VIB of Vietnam International Commercial Bank decreased by 2.28% and SSI of brokerage SSI Securities Corporation slid 2.19%.
Foreign investors were net sellers to the tune of VND1.227 trillion, mainly selling VHM of property giant Vinhomes and VNM of dairy giant Vinamilk.
The HNX-Index for stocks on the Hanoi Stock Exchange, home to mid and small caps, fell 0.79% while the UPCoM-Index for the Unlisted Public Companies Market slid 0.28%.